Remove test scene from build settings and codebase. (#3524)

Project/ProjectSettings/EditorBuildSettings.asset

 EditorBuildSettings:
   m_ObjectHideFlags: 0
   serializedVersion: 2
-  m_Scenes:
-  - enabled: 1
-    path: Packages/com.unity.ml-agents/Tests/Runtime/SerializeTestScene.unity
-    guid: 60783bd849bd242eeb66243542762b23
+  m_Scenes: []
   m_configObjects: {}

com.unity.ml-agents/Tests/Runtime/SerializationTest.cs.meta

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-  icon: {instanceID: 0}
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com.unity.ml-agents/Tests/Runtime/SerializeAgent.cs.meta

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com.unity.ml-agents/Tests/Runtime/Unity.ML-Agents.Runtime.Tests.asmdef

-{
-    "name": "Unity.ML-Agents.Runtime.Tests",
-    "references": [
-        "Unity.ML-Agents"
-    ],
-    "optionalUnityReferences": [
-        "TestAssemblies"
-    ],
-    "includePlatforms": [],
-    "excludePlatforms": [],
-    "allowUnsafeCode": false,
-    "overrideReferences": false,
-    "precompiledReferences": [],
-    "autoReferenced": true,
-    "defineConstraints": []
-}

com.unity.ml-agents/Tests/Runtime/Unity.ML-Agents.Runtime.Tests.asmdef.meta

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com.unity.ml-agents/Tests/Runtime/SerializationTest.cs

-// using System.Collections;
-// using NUnit.Framework;
-// #if UNITY_EDITOR
-// using UnityEditor.SceneManagement;
-// using UnityEngine.TestTools;
-// #endif
-// using UnityEngine;
-// using UnityEngine.SceneManagement;
-//
-// namespace Tests
-// {
-//     [TestFixture]
-//     public class SerializationTest
-//     {
-//
-//         [SetUp]
-//         public void Setup()
-//         {
-//             SceneManager.LoadScene("Packages/com.unity.ml-agents/Tests/Runtime/SerializeTestScene");
-//         }
-//
-//         /// <summary>
-//         /// Test that the serialized agent in the scene, which has its agent parameter value serialized,
-//         /// properly deserializes it to Agent.maxStep.
-//         /// </summary>
-//         [UnityTest]
-//         public IEnumerator SerializationTestSimplePasses()
-//         {
-//             // Use the Assert class to test conditions
-//             var gameObjects = SceneManager.GetActiveScene().GetRootGameObjects();
-//             if (SceneManager.GetActiveScene().name != "SerializeTestScene")
-//             {
-//                 yield return null;
-//             }
-//
-//             GameObject agent = null;
-//             foreach (var go in gameObjects)
-//             {
-//                 if (go.name == "Agent")
-//                 {
-//                     agent = go;
-//                     break;
-//                 }
-//             }
-//             Assert.NotNull(agent);
-//             var agentComponent = agent.GetComponent<SerializeAgent>();
-//             Assert.True(agentComponent.maxStep == 5000);
-//
-//         }
-//     }
-// }

com.unity.ml-agents/Tests/Runtime/SerializeAgent.cs

-using System.Collections;
-using System.Collections.Generic;
-using UnityEngine;
-using MLAgents;
-
-public class SerializeAgent : Agent
-{
-    public override float[] Heuristic()
-    {
-        return new[] {0f};
-    }
-}